Let’s start with the old-school way of collecting data for weather forecasts. It’s 6:30 in the morning at a National Weather Service post in Sterling, Virginia.

“What we’re doing now is getting the helium to flow into the balloon,” says meteorologist Kevin Witt as he inflates a six foot latex weather balloon.

These balloons float into the sky twice a day, from about 90 sites, carrying instruments that send back pressure, temperature, and humidity data. They go high – about 19 miles high – transmitting data as the balloon expands to the size of a small building and ultimately pops. The instrument, called a radiosonde, floats back to earth on a little orange parachute.

The NWS Sterling office is near Dulles International Airport, so Witt calls the tower before releasing the balloon.

It just so happens, there could be planes flying through Dulles that are also collecting weather data. The government has long partnered with airlines to measure temperature and wind during flights. More recently, Southwest Airlines and UPS Airlines have installed sophisticated sensors that measure water vapor, like balloons do.

But unlike balloons, which provide a data snapshot over a shorter time, planes create a moving picture as they take off and land, then take off and land again. They transmit humidity data every few seconds upon ascent, every few minutes at cruising altitude, and multiple times a minute while landing. According to the National Oceanic and Atmospheric Administration, the ascent and descent data are compiled into profiles for each flight, whether it's a long haul or a short jump.

“Without the aircraft observations, the models are only receiving data every 12 hours,” says Steve Pritchett, program manager for the National Weather Service Aircraft Observation Program.

Remember, weather balloons launch twice a day. So let’s say a thunderstorm is projected to hit Dulles at 3pm. A plane might send real time info that no, the air mass is drier -- No storm likely.

“And I don’t have to wait 12 hours to determine that,” Pritchett says. “I can see it because I have an observation coming in this hour from an aircraft.”

He says major airports in Los Angeles, Seattle, and Houston don’t even have upper-air balloon launches within one hundred miles. But they do have Southwest Airlines. Its chief meteorologist Rick Curtis says the company has equipped 87 planes with water vapor sensors, with 19 more in the pipeline. He says the technology is working.

“In late November of this past year, we were able to use that information to determine whether or not an ice storm was gonna affect Dallas,” he says.

That’s Dallas, Texas, not Dulles. Curtis says Southwest looked at the atmospheric data, saw less moisture and some warmer layers, then kept flying.

“It saved the mass, wholesale cancellations of an event like that,” he says. “Something that’s commonplace when you see an ice storm come to a southern city.”

And that saves money. Economist Kevin Neels of the Brattle Group worked on a study that found delays directly cost airlines $8.3 billion in 2007. That’s not including the cost to passengers.

“We estimated that the cost to the people was twice as much as the cost to the airlines,” he says.

Right now, the government pays for the water vapor sensors. Steve Pritchett of the National Weather Service says it’s worth it. He wishes all planes were equipped with them. The only drawback of relying on planes for data, he says, is he can’t tell them where to fly.